The Environmental Protection Agency has recently published proposed guidelines, procedures, emission standards and equipment specifications for inspection maintenance (ASM) equipment; EPA Acceleration Simulation Mode Draft Procedures, Emission Standards, Quality Control Requirements, and Equipment Specifications, dated Nov. 28, 1995, Version 15.6. The State of California has also proposed new, more stringent regulations in California BAR Automotive inspection & Repair, Equipment for Test & Repair, Dec. 15, 1995. Similar regulations are currently required in areas of the United States which are deemed non-attainment areas with excess air pollution levels.
These regulations, inter alia, set up new specifications for calibrating and zeroing emissions test equipment and require that the instruments be zeroed before each test using pure nitrogen or purified air, referred to as zero grade air. The proposed specifications define the purity of zero grade air as follows:
Concentration: 20.7%.+-.0.5% Oxygen with Balance Nitrogen
Impurities:
less than 1 ppm Total hydrocarbons PA1 less than 1 ppm Carbon Monoxide PA1 less than 1 ppm Oxides of Nitrogen PA1 less than 1 ppm Carbon Dioxide PA1 less than 500 ppm total hydrocarbons PA1 less than 200 ppm carbon monoxide PA1 less than 25 ppm oxides of nitrogen
Low cost emissions test equipment (i.e. California BAR-90 type) employ background ambient air to zero the gas analyzers. However, the proposed equipment specifications, among other things, require several times more sensitivity from the test equipment and consequently, require a more pure source of zero air to achieve a more accurate measurement at these new low levels of measurement. The proposed ASM specification for instrument air corresponds very closely to the EPA IM-240 zero air specification currently in use in certain areas, including the non attainment areas, of the United States.
Currently only two methods, bottled zero air or zero air generators, are being used to produce the aforementioned zero grade air. The zero air generators used for emissions test purposes are designed for very high flow rates, i.e. greater then 40 liters/minute, and are typically only used in facilities with multiple test lanes which can support the zero air generator cost as compared to the cost of bottled air. Multiple lane zero air generators are expensive and can range in cost from $10,000 to $16,000 per generator , depending on the flow rate of the generator. Bottled air, although satisfactory for the purpose, necessitates the expense and inconvenience of storing pressurized containers and can result in down time if new supplies are not timely reordered.
Many current methods exist to easily and cost effectively filter shop air (compressed air) and reduce background air concentrations of hydrocarbons and carbon monoxide to some extent. However, the existing methods and apparatus do not cost effectively provide for purification of background ambient air according to proposed emission test standards.
For example, most filtration methods will not adequately reduce the concentrations of oxides of nitrogen to less than 1 ppm nitric oxide.
Accordingly it is an object of this invention to provide a low cost method and apparatus for the production of zero air for use in the analysis of vehicle exhaust omissions and instrumentation for analytical laboratory gas measurement, such as, for example, flame ionization detectors (FID) and chemiluminescence analyzers (CLD).